At the present time, physicians often treat patients with atrial fibrillation (AF) using radiofrequency (RF) catheter systems to ablate conducting tissue in the wall of the left atrium of the heart around the ostium of the pulmonary veins. Similar technology, using radiofrequency energy, has been used inside the renal arteries to ablate sympathetic and other nerve fibers that run in the outer wall of the renal arteries, in order to treat high blood pressure. In both cases these are elaborate and expensive catheter systems that can cause thermal, cryoablative, or other injury to surrounding tissue. Many of these systems also require significant capital outlays for the reusable equipment that lies outside of the body, including RF generation systems and the fluid handling systems for cryoablative catheters.
Because of the similarities of anatomy, for the purposes of this disclosure, the term target vessel ostial wall will refer here to either the wall of the pulmonary vein near the left atrium for AF ablation applications or the wall of the renal artery near the aorta for hypertension therapy applications. It is anticipated that ablation of nerve fibers for renal sympathetic denervation could be performed more distally as well.
In the case of atrial fibrillation ablation, the ablation of tissue surrounding multiple pulmonary veins can be technically challenging and very time consuming. This is particularly so if one uses RF catheters that can only ablate one focus at a time. There is also a failure rate using these types of catheters for atrial fibrillation ablation. The failures of the current approaches are related to the challenges in creating reproducible circumferential ablation of tissue around the ostium (peri-ostial) of a pulmonary vein. There are also significant safety issues with current technologies related to very long fluoroscopy and procedure times that lead to high levels of radiation exposure to both the patient and the operator, and may increase stroke risk in atrial fibrillation ablation.
There are also potential risks using the current technologies for RF ablation to create sympathetic nerve denervation inside the renal artery for the treatment of hypertension. The short-term complications and the long-term sequelae of applying RF energy inside the renal artery itself are not well defined. This type of energy applied within the renal artery may lead to late restenosis, thrombosis, embolization of debris into the renal parenchyma, or other problems inside the renal artery. There may also be uneven or incomplete sympathetic nerve ablation, particularly if there are anatomic abnormalities, or atherosclerotic or fibrotic disease inside the renal artery, such that there is non-homogeneous delivery of RF energy. This could lead to treatment failures, or the need for additional and dangerous levels of RF energy to ablate the nerves that run along the adventitial plane of the renal artery.
The Bullfrog® micro infusion catheter described by Seward et al in U.S. Pat. Nos. 6,547,803 and 7,666,163 which uses an inflatable elastic balloon to expand a single needle against the wall of a blood vessel could be used for alcohol injection but it would require multiple uses as it cannot deliver an ablative substance around the entire circumference of the vessel. The most number of needles shown by Seward is two and the two needle version of the Bullfrog® would be hard to make small enough to fit through a guiding catheter into a renal artery. If only one needle is used, accurate rotation of any device at the end of a catheter is difficult at best and could be risky if the subsequent injections are not evenly spaced if the rotation is off. Another limitation of the Bullfrog® is that inflation of a balloon within the renal artery can induce restenosis due to balloon injury as well as the removal of the protective layer of endothelial cells. Finally, while injection of ethanol as an ablative substance is well known and used within the heart and other parts of the body, there has been no development of an ethanol injection system specifically designed for the circumferential ablation of sympathetic nerve fibers around the renal arteries.